Elongated sheet or stock material is used in the manufacturing of a variety of products including paper cups. Normally this sheet material is shipped and stored in the form of a roll or coil and, therefore, must be unwound to be used. Unwinding stands for rotatively supporting one or more rolls provide a simple means of feeding the web of material to the next phase of the particular manufacturing process. Usually, however, only one roll of material can be fed to the next phase and, consequently, when this roll is exhausted, the manufacturing process must be stopped so that the depleted roll can be removed and replaced by a new roll. The time spent unloading the depleted roll and properly loading the new roll results in a loss of production of the final product. As a result, numerous machines have been developed to support two rolls of material so that one roll may be unwound while the other roll is prepared and positioned for movement into an unwinding position after the first roll is depleted.
For example, U.S. Pat. No. 2,267,962 to Tishken discloses a coil holder having two roll receivers adjacent each other for holding two coils of material so that one roll can be unwound while another roll is loaded for unwinding. The roll receivers are mounted on a movable carriage which is shifted laterally relative to the direction in which the web is unwinding to position a full new roll into the unwinding position when one roll is exhausted. Thus, this machine minimizes the unloading time by limiting the delay to the time involved in moving the carriage a short distance and connecting the end of the web of the material on the full roll to the machine downstream in the process. However, this stand does not provide a simple means for maintaining the alignment of the web in the unwinding position.
Once a roll of material is properly positioned and unwinding has begun, it is usually desirable to maintain the edges of the material in alignment with some predetermined path dictated by a machine or device receiving the sheet material from the unwinding stand. Normally misalignment is caused by the web wandering laterally with respect to the its direction of unwinding and may lead to excessive waste of material, and low quality or possibly useless final products. As a result, a variety of web alignment devices for unwind stands have been designed to detect and correct the misalignment.
For example, U.S. Pat. No. 3,997,094 to Aylesworth discloses an edge alignment device using detectors for sensing the edge of a sheet material being unwound from a coil and actuating hydraulic cylinders for laterally moving the coil to maintain the sheet material in a desired alignment. U.S. Pat. Nos. 3,262,650 to Randich and 4,073,448 to Kolosov both disclose alignment devices including an air cylinder for fine positioning a roll of a web material along the central axis of the roll. Similarly, U.S. Pat. No. 4,077,579 to Seleski et al. discloses an automatic edge alignment apparatus using a photo-electric edge detector for controlling a bi-directional solenoid adapted to shift a carriage laterally to maintain web alignment. However, none of these edge alignment devices is used in conjunction with an unwind stand which permits a stand-by roll of material to be prepared and positioned for quick and easy movement into the unwinding position.
Another important function of some types of unwind stands is the ability to apply a braking force to the sheet material as it is withdrawn from the roll. This is often performed by a braking device which maintains a desired amount of tension on the material so that only the required amount of material is unwound or pulled from the roll. Since the material is pulled by the machine receiving the web from the unwind stand, without any such tension, the roll of material may rotate faster than required releasing more material from the roll than the receiving machine is ready to accept. One such tensioning device is disclosed in U.S. Pat. No. 2,596,428 to O'Malley. This device includes a brake wheel which is urged against the periphery of the roll of material and a threaded member for adjusting the braking force. Also, U.S. Pat. No. 2,991,849 to Erickson discloses a friction brake apparatus in which brake shoes are urged with variable force against a drum or disk rotating with a coil of material.
Thus, the prior art fails to disclose an unwind stand for web material which simply and effectively permits the unwinding of a first roll of material and the simultaneous loading or unloading of a second roll for quick and easy movement into the unwinding position while maintaining the alignment of the unwinding material as it is unwound.